1. Field of the Invention
This invention generally relates to the interconnection of pipes and more specifically for fittings or apparatus for connecting individual pipes into a pipe system.
2. Description of Related Art
Many pipe systems include a main pipe and a plurality of subsidiary pipes that in various applications may be called service, lateral or branch pipes. In the following discussion the phrase "lateral pipe" means any such subsidiary pipe that connects to a main pipe at a tap hole through the main pipe wall. In some systems liquid flows from the main pipe, as a supply pipe or manifold, to lateral pipes; in others, from lateral pipes to the main pipe as a collector or return pipe. Such pipe systems may be installed above or below ground. The pipes may be formed of a wide variety of materials including plastics (polyvinylchloride is typical), thermoplastics, metal and concrete.
It is important to connect such lateral and main pipes with a leakproof connection. In sewer systems, for example, such connections are required to prevent sewage from leaking into the ground and, as importantly, ground water from infiltrating the sewer system. It also important the apparatus for making such connections be simple to install in the field, particularly in pipe systems having pipes of large diameter and weight.
This invention particularly relates to a class of pipe fittings called "saddle tee" fittings. Basically a saddle tee fitting has a saddle portion for overlying a portion of a main pipe and a cylindrical extension, called a "tee", that receives the end of a lateral pipe. The saddle is intended to form a seal with the main pipe and the tee, with the lateral pipe. The tee may extend at any angle from an axis of the main pipe, angles of 90.degree., 60.degree. and 45.degree. being typical.
There are a number of features that should characterize a saddle tee fitting. The fitting must produce a leakproof seal to prevent flow both into and out of the pipe system (i.e., to prevent leaking and ground water filtration). The fitting must be durable and withstand the environment. The fitting must be easy to install, preferably without any requirement for special tooling at an installation site. The fitting should not impede or otherwise alter the flow characteristics in the pipe system. One single saddle tee fitting sized for a given lateral pipe should connect to main pipes of different diameters in order to reduce inventory requirements.
U.S. Pat. No. 2,736,335 of Webber for "Tapping and Cutoff Connection to Plastic Fluid Pressure Main" discloses a saddle fitting for plastic pipe. A saddle connects to a main pipe by suitably wetting counterfacing surfaces with an adhesive, typically a plastic solvent, and by clamping the saddle to the pipe until a plastic bond forms.
U.S. Pat. No. 4,606,558 to Davidson for "Plastic Pipe Fitting" discloses a saddle fitting with a perforated saddle and a tee that extends from the saddle. During assembly a solvent coats the interface of the saddle and the main pipe. A clamping tool attaches to bosses at each end of the saddle to clamp the saddle firmly to the main pipe until plastic flows through the perforations and forms rivet-like structures that permanently bond the saddle to the pipe. Then the clamping tool can be removed.
U.S. Pat. No. 3,649,055 to Neilson for "Clamp Fitting With Seal For Plastic Pipe" discloses a fitting with a saddle body that snaps to a main pipe after counterfacing surfaces of the pipe and saddle are coated with a plastic or adhesive. When the saddle snaps onto the pipe, the saddle provides the necessary clamping forces to position the saddle until the solvent or adhesive sets. An O-ring or similar sealing device in a circumferential groove of the saddle provides a seal around a tap hole through the main pipe.
In U.S. Pat. No. 4,894,521 to Evans for "Electric Heating Element For Fusing Thermoplastic Materials" a saddle contains an integral heating element. The saddle seals to a pipe of thermoplastic materials when the element heats. This produces a permanent seal between the saddle and the pipe.
Each of the foregoing references discloses saddle tee fittings in which a permanent bond forms between the saddle and the main pipe. This bond depends upon the ability of the materials in the pipe and saddle to commingle or fuse. Each requires special materials in the form of solvents or heaters. It is not possible to obtain such a joint in sewer systems comprising concrete or ductile iron pipes. Even if it were possible to make such joints in these materials, the requirements for special tools and materials would minimize the desirability of the joints with respect to sewer systems.
U.S. Pat. No. 3,188,121 Cude et al for "Cable Sheath Pressure Tap Fitting" discloses a saddle tee structure that enables the formation of a tap for a high pressure line containing electrical conductors or the like. The saddle tee fitting is rubber or plastic while the pipe has an outer sheath of lead or other weather resistant material. The saddle includes an underlying gasket preferably with an adhesive backing for adhering to the pipe. A tape wrap overlies the saddle portion and pipe thereby to hold the saddle against the pipe. In this structure a small gap exists in the tape along the axially extending edges of the saddle that are coextensive with the tee structure. In the Cude et al patent this is a small gap. If this approach is applied to other pipe systems, that gap will approximate the diameter of the lateral pipe gap and can be up to 4" or more. It becomes difficult to maintain a seal across gaps of these proportions. Cude et al also suggest substituting hose clamps for the tape wrap. Such a substitution would not reduce any gap; indeed the gap might increase in length.
British Patent No. 852,326 to Collins for "Improvements in Pipe Connections" discloses another embodiment of a saddle tee fitting. The fitting comprises an integral base and flange formed of plastic or the like. The tee portion of this fitting is internally or externally threaded. Given the materials suggested for construction, a requirement for a separate sealing gasket and the use of rigid straps (cast iron is preferred), it must be concluded that this fitting is rigid. It does not distort to any significant or practical degree. Consequently, it is only possible to connect a given fitting to a main pipe of a given size. Moreover, this structure requires a significant number of component parts that are specially formed thereby increasing the costs of the fitting and the complexity of installation.
U.S. Pat. No. 4,494,780 to Burnett for a "Liquid Piping Saddle Assembly Connecting A Branch Pipe to a Main Pipe" discloses a generally cylindrical elastomeric tee with one end preformed to attach to a main pipe of different sizes. A shoulder in the exterior of the tee provides a bearing surface for a rigid collar or casting. A flexible strap, when tightened, pulls the casting over the tee against the shoulder to drive the tee against the main pipe and produce a seal. This process deforms the tee adjacent the main pipe. Moreover, the internal structure of the tee includes another shoulder that spaces the end of a lateral pipe from the main pipe. Consequently a pocket forms that can collect debris and eventually restrict flow through the connection.
U.S. Pat. No. 4,966,397 of McKinnon for "Flexible Pipe Saddle" discloses a flexible saddle tee fitting that uses spaced hose clamps to affix a saddle to a pipe. As described later with respect to FIGS. 1 and 2, this saddle tee fitting includes a rectangularly shaped saddle that flexes about an axis that is coincident with the longitudinal main pipe axis, but is relatively rigid in other directions, particularly along the axially extending edges of the saddle parallel to the main pipe axis. Two clamping bands encircle the main pipe at the axial ends of the saddle. The spaced clamping bands leave a gap along the axial edge of the saddle. Although this edge contains a stiffening device, it is still difficult to guarantee seal integrity along this entire gap.
U.S. Pat. No. 5,020,832 to Coblentz for a "Flexible Pipe Saddle" discloses a saddle tee assembly with a flexible resilient polymer saddle tee, an overlying flexible metallic skirt and a plurality of clamping bands. The saddle tee has a flexible skirt portion that conforms to a main pipe about an opening and a cylindrical tee portion for receiving a lateral pipe. A radially-extending, bevelled annular shoulder formed inside the tee receives the end of the lateral pipe. Three clamping bands encircle the flexible metal skirt and main pipe to effect a seal.
Saddle tee fittings for attachment to differently sized main pipes, like those described in the Burnett, McKinnon and Coblentz patents, typically are molded to a nominal pipe size. For example a saddle tee for receiving a six-inch lateral pipe might be molded for attachment to a ten-inch main pipe as a nominally sized pipe even though the saddle tee could be connected to larger and smaller main pipes. When a saddle tee is attached to a main pipe of nominal size, the tee portion forms a cylindrical passage. Internal, radial or bevelled shoulders remain in a radial plane, so they contact the end of the lateral pipe. Moreover, the tee is readily sealed to the lateral pipe when it is cylindrical.
When the saddle tee is fitted to main pipes of different sizes, the tee portion distorts into an oval shape. As the main pipe diameter increases from the nominal diameter, the tee deforms into an oval cross section with a major axis parallel to an axis of the main pipe. As the main pipe diameter decreases from the nominal diameter, the tee deforms into an oval cross section with a major axis at right angles to the axis through the main pipe. Such distortions make it more difficult to guarantee a seal between the tee and the lateral pipe. These distortions produce concave or convex distortions in the internal, radial or bevelled, shoulder that normally engages the end of the lateral pipe. Consequently axial gaps exist between the shoulder and lateral pipe. These gaps can trap entrained solid materials flowing through the pipe and eventually alter or impede flow.